Negative voltage regulator adapted to be constructed as an integrated circuit

ABSTRACT

A temperature-compensated, ripple-reducing negative voltage regulator which is adapted to be constructed as an integrated circuit in that no inductors and a minimum number of capacitors are used and any PNP transistors that are used need not have good current amplification factors. The regulator includes protection against excessive current and momentary excessive voltages.

United States Patent mm Wm w w mO r. 3mm. m na UMMBB 77900 66677 99999 11111 l/l/l 00 5400 1 11285 49042 2 1 3394 3 1 ,5 33333 f 0 m o b m m m M r w m n D F F M a! 2 mmmam eh 5 WTTA3 m o m N m m V D. .m A 1 2 l 7 2 323/22 T 323/22 T 323/22 T OTHER REFERENCES 22 Filed May 8,1970

Electronic Design, Half-amp Voltage Regulator Fits on a Chip," Vol. 16, No.5, March 1, 1968, Pg. 28, TK 7800 E51.

[45] Patented Oct. 12, 1971 [7 3] Assignee Motorola, Inc.

Franklin Park, Ill.

Primary Examiner-A. D. Pellinen mm @C mm mm mm Mm Sh m n mam T Cm VUD EH V um. A h fi NBB M ABSTRACT: A temperature-compensated, ripple-reducing negative voltage regulator which is adapted to be constructed as an integrated circuit in that no inductors and a minimum number of capacitors are used are used need not have [51] Int.

and any PNP transistors that good current amplification factors. e regulator includes protection against excessive current 323/9 and momentary excessive voltages.

[5 6] References Cited UNITED STATES PATENTS 3,305,764 2/1967 Todd...................

ELECTRONlC TURN OFF DROP LOA

I l I l l PAIENTEDncI 12 I97! .lllllllllr-I'Illllllllllllll-ll..- Ill I N VENTOR. Will/am Folsom Dav/s BY Thomas M. Frederiksen Arrrs.

NEGATIVE VOLTAGE REGULATOR ADAPTED TO BE CONSTRUCTED AS AN INTEGRATED CIRCUIT BACKGROUND When putting a negative voltage regulator on a chip, that is, when a negative voltage regulator is constructed as an integrated circuit (hereinafter lC), the obvious way to do this would be to adapt a positive voltage regulator for regulating negative voltage by changing all the dominantly NPN transistors included in an already existing positive voltage regulator to dominantly PNP transistors. However, at this state of the art, it is very difficult to produce good PNP transistors as part of an IC. Furthermore, even though the characteristics of transistors and diodes may vary with temperature, it is advantageous for the characteristics of the completed regulator to be temperature independent. It is also advantageous for the negative voltage regulator comprising the [C to exhibit good rejection of ripple on the input line and low output impedance over a wide frequency range, whereby the regulator can supply current which changes very rapidly. The regulator should be capable of a large output voltage range, should include short circuit protection and should have provisions for shutting it down by applying a voltage to an element thereof.

SUMMARY OF THE INVENTION In accordance with this invention, the regulator, as put on a chip, is comprised of a temperature-regulated standard or reference voltage-producing section coupled to a reference voltage-shifting section which is itself coupled to a main voltage control section. The regulator includes NPN transistors to a great extent. Many of the constituent transistors on which ripple voltage may be impressed are placed in the circuit such that they have high output impedance to reduce the rippled feedthrough from the input line to the output. The output impedance of the regulator is very low and loads which require quickly varying currents at a regulated voltage may be supplied. Furthermore, short-circuit protective features are built into the regulator.

DESCRIPTION The regulator will be better understood upon reading the following description in connection with the sole FIGURE of the accompanyingdrawing which illustrates a negative voltage regulator including an embodiment of this invention.

In the single figure, all the circuit elements and their connections which are within the dotted rectangle are deposited on a chip to form an IC. For supply, for control and adjustment, for filtering, for frequency compensation, for connection to a load and for versatility of operation, several external connections are provided for the chip. The unregulated negative input supply may be connected to the terminal 12. A resistor 14 whose value limits the short circuit current supplied by the regulator is connected between he terminals 12 and 16. A resistor 18 is connected between the tenninal 20 and the terminal 22, and a resistor 24 is connected between the terminal 22 and the ground terminal 26 for the purpose of determining the regulated voltage applied to the load. For convenience, the grounded end of the external elements such as the resistance 24 are shown connected to a ground symbol rather than to the ground terminal 26. The load 28 is connected between both the load voltage-sensing terminal 30 and the load current supply terminal 32 and ground. A filtering and amplifier stabilizing capacitor '34 is also connected across the load 28. In addition, a capacitor 174 can be placed between terminal 21 and terminal 16 for stabilizing this amplifier. Thus this amplifier can be compensated in two different manners. Another filtering and amplifier stabilizing capacitor 36 is connected between the terminal 38 and the ground terminal 26 for stabilizing another amplifier. The regulator on the chip may be turned off by applying a negative voltage with respect to terminal 26 to the terminal 40. The voltage across the load is also equal to the voltage at the terminal 20. If the load 28 is very close to the chip, whereby the voltage drop in the lead to the load is very small, the voltage-sensing terminal 30 and the current supply terminal 32 are connected together as shown. In the case that the negative voltage regulator to be described is at a distance from the load, whereby the voltage drop in the lead between both terminals 32 and 30 and the load may cause bad voltage regulation at the load (although the voltage regulation at the terminals 30 and 32 may be good), two conductors may be provided, one between the terminal 30 and the ungrounded terminal of the remote load; the other between terminal 32 and the ungrounded terminal of the remote load. Since very little current flows (base current of transistor 136) in the current-sensing lead, that is, the lead that is connected to the terminal 30, the voltage drop in this lead will remain very low, essentially independent of the current requirements of the load. Therefore, by placing the load voltage sensing terminal 30 at the load, the voltage at the load is regulated without regard to the losses in the long lead from the current supply terminal 32 to the load.

The elements on the chip and their connections will now be described. The terminal 12 is connected through a resistor 42 and a Zener diode 44 in series to the ground terminal 26. The junction of the resistor 42 and the Zener diode 44 is connected by way of the resistor 46 to the emitter of an NPN transistor 48 whose base is connected to the collector of an NPN transistor 50 and whose collector is connected to the collector of an NPN transistor 52. The junction of the resistor 42 and the Zener diode 44 is also connected through a resistor 54 to the emitter of an NPN transistor 56. The base of the transistor 56 is connected to the collector of the transistor 50 and to the anode of a Zener diode 58, whose cathode is connected to ground. The collector of the transistor 56 is connected to the base of an NPN transistor 60.

The emitter of the transistor 50 is connected to the terminal 12 by way of a resistor 62, and its collector is connected to the cathode of a diode 64 whose anode is connected through two resistors 66 and 68 in series to the cathode of a diode 70. The anode of the diode 70 is connected to the cathode of a diode 72 and the anode of a diode 72 is connected to the base of the transistor 60 and through the resistor 74 to ground. The collector of the transistor 60 is connected directly to ground and its emitter is connected to the base of an NPN transistor 76. The collector of the transistor 76 is connected to ground by way of a resistor 78 and to the anode of a diode 80. The emitter of the transistor 76 is connected to the collector of an NPN transistor 52, to the base of a PNP transistor 84, to the collector of the transistor 48, and to the collector of a PNP transistor 82. The bases of the transistors 50 and 52 are connected together and to a base line 51. The emitter of transistor 52 is connected to the terminal 12 by way of a resistor 86. The base of the transistor 82 is connected to ground by way of a resistor 88 and to the turnoff terminal 40. The emitter of the transistor 82 is connected directly to ground.

The collector of the transistor 84 is connected to the base of an NPN transistor 90 and to the anode of a diode 92. The emitter of transistor 84 is connected to the cathode of diode 80. The cathode of the diode 92 is connected to the anode of a diode 94. The cathode of the diode 94 is connected to the terminal 12 by way of a resistor 96. The emitter of the transistor 90 is connected to the base line 51 and the collector of the transistor 90 is connected directly to ground.

The junction of the resistors 66 and 68 is connected to the base of an NPN transistor 98, whose collector is connected directly to ground and whose emitter is connected to the base of an NPN transistor 100, the collector of the transistor being connected directly to ground and its emitter being connected to the emitter of an NPN transistor 102 and to the collector of an NPN transistor 104. The base of the transistor 104 is connected to the base line 51. The emitter of the transistor 104 is connected to the terminal 12 by way of a resistor 106. The collector of the transistor 102 is connected to ground by way of a resistor 108. The base of the transistor 102 is connected to the emitter of an NPN transistor 110, whose collector is connected to ground and whose base is connected to the terminal 22.

The collector of the transistor 102 is also connected to the emitter of a PNP transistor 112. The collector of the transistor 112 is connected to the anode of a diode 114 and through a resistor 116 to the terminal 38. The base of the transistor 112 is connected to the base of a PNP transistor 118 and to the emitter of an NPN transistor 119. The cathode of the diode 114 is connected to the base of an NPN transistor 120 whose collector is connected directly to ground and whose emitter is connected to the tenninal and also to the collector of an NPN transistor 122. The base of the transistor 122 is connected to the base line 51. The emitter of the transistor 122 is connected to the terminal 12 by way of a resistor 124. The cathode of the diode 114 is also connected to the collector of a transistor 126, whose base is connected to the base line 51 and whose emitter is connected to the terminal 12 by way of a resistor 128. The cathode of the diode 114 is also connected to the collector of a PNP transistor 130 whose base is connected to the anode of a diode 132. The emitter of the transistor 130 is connected to the cathode of a diode 134 and to the base of an NPN transistor 136. The anode of the diode 134 and the cathode of the diode 132 are connected to the base of an NPN transistor 138 and to the external output reference terminal 20. The collector of the transistor 119 is connected to ground and the emitter of the transistor 119 is connected to the collector of an NPN transistor 142, whose base is connected to the base line 51 and whose emitter is connected to the terminal 12 by way of a resistor 144. The base of the transistor 119 is connected to ground by way of a resistor 146 and to the collector of an NPN transistor 1, whose base is connected to the base line 51 and whose emitter is connected by way of a resistor 150 to the terminal 12.

The emitters of the transistors 136 and 136 are connected together and to the collector of an NPN transistor 152 whose base is connected to the base line 51 and whose emitter is connected to the terminal 12 by way of a resistor 154. The collector of the transistor 138 is connected to the emitter of the transistor 118 and to ground through a resistor 156. The collector of the transistor 136 is connected directly to ground. The base of the transistor 136 is connected to the voltagesensing output terminal 30.

The collector of the transistor 118 is connected to the base of an NPN transistor 158 and to the anode of a diode 160 and to the collector of an NPN transistor 162 and ma compensation terminal 21. The base of the transistor 162 is connected to the base line 51 and the emitter of the transistor 162 is connected to terminal 12 by way of the resistor 164. The collector of the transistor 148 is connected to the regulated voltage and current supply output terminal 32. The emitter of the transistor 158 is connected to the base of an NPN transistor 166 whose collector is connected to the terminal 32 and whose emitter is connected to the terminal 16. The cathode of the diode 160 is connected to the anode of a diode 168. The cathode of the diode 168 is connected to the anode of a diode 170. The cathode of the diode 170 is connected to the anode of a diode 172, and the cathode of the diode 172 is connected to the terminal 12.

The operation of the circuit as shown and described will now be explained. The circuit as described includes components for turning the described negative voltage regulator ON. This is referred to as the start circuit. When the terminal 12 is connected to an unregulated negative voltage supply, the Zener diode 44 will break down putting the emitter of the transistor 48 at a regulated negative voltage of about minus 7 volts. Since the base of the transistor 48 is initially at ground potential, current will initially at ground potential, current will initially be provided for the base of transistor 48 rendering it conductive to supply initial base drive for transistor 84. At the same moment, the 7-volt negative voltage will also be applied to the emitter of the transistor 56 and, since there also is zero volts initially on the base thereof, current will flow to thebase of the transistor 56 which will cause current to flow in the resistor 74 establishing an initial voltage drop across this resistor. The base current for the transistor 60 is also supplied by the current in resistor 74. This conduction of the transistor 60 supplies base current for the transistor 76, causing some current to flow through the resistor 78 and partially satisfying the current demanded by the collector of transistor 48. The remaining collector current of transistor 48 serves as base current for transistor 84. The actual voltage drop across resistor 78 is approximately equal to the voltage drop across resistor 74 since the sum of the base emitter drops of transistors 60 and 76 minus the sum of the base emitter drops across transistor 84 and forward voltage drop across diode is approximately zero. The collector current flowing in transistor 84 is approximately equal to the current flowing in resistor 78 minus the collector current of transistor 48. The collector current of transistor 84 supplies base current to the transistor as well as producing a voltage drop across resistor 96. The transistor 90 will supply base current for the transistors 50, 52, 104, 122, 126, 148, 142, 152 and 162 since they are all connected by the base line 51. When all of these transistors are ON" the regulator is said to be ON and there is, from then on, no need for the start circuit since there is now a circuit for the emitter and base current of the transistors 76 and 84 respectively, that does not include the transistor 48 and for the current flowing through resistor 74 which does not include transistor 56. This occurs since the base current of transistor 52 renders its collector conductive to supply base current for the transistor 84. Also since transistor 50 is conductive, current flowing in the collector path of the transistor 41) forces the Zener diode 58 to break down as well as to provide current through resistor 74, eliminating the need for the transistor 56. The resistors 46 and 54 are provided to cause current flow equalization in the transistor 48 and 56 when conductive. As soon as the Zener diode 58 breaks down, there is no voltage between the base and the emitter of the two transistors 48 and 56 and the transistors 48 and 56 act as if they were not there.

The chip includes a zero temperature coefficient circuit 59. This circuit 59 includes two branches; one branch comprising the Zener diode 58 which has a positive temperature coefficient of voltage, and the other branch comprising the three diodes 64, 70 and 72 which have a negative temperature coefficient of voltage and the three resistors 66, 68 and 74 which have a positive temperature coefficient of resistance. As is known, the Zener diode 58 in breakdown provides a substantially constant voltage thereacross and the voltage at the junction of the resistors 66 and 68 is almost exactly constant with respect to terminal 26 (ground) in spite of variations of temperature of the chip on which the regulator is deposited and in spite of variations in voltage applied to the terminal 12 as long as the current flow through both branches of the approximately constant.

The transistor 50, as well as all other transistors which are connected to 'the base line 51, acts as a constant current means. This is accomplished as follows: The current through the resistor 74 is essentially constant with temperature which is characteristic of the current through the reference network 59. Due to the connections of the emitter of the transistor 60 to the base of the transistor 76, very little current is required to drive the transistor 76 whereby the transistor 60 applies very little loading to the resistor 74 which is desired. The voltage drop across the resistor 78 is approximately equal to the voltage drop across the resistor 74 since the base-to-emitter voltage drop of the transistor 60 added to the baseto-emitter voltage drop in the transistor 76 balances the voltage drop in the base to emitter of the transistor 84 plus the cathode-toanode voltage drop in the diode 80. Since the voltage drop across the resistor 78 is related to the voltage drop across re sistor 74, the current flowing through resistor 78 is also constant, independent of temperature. Furthermore, the current flowing out of the collector of the transistor 84 is approximately equal to the current in resistor 78 minus the collector current of transistor 52. The current through the collector of circuit 59 is transistor 84 is passed through the diodes 92 and 94 and through the resistor 96 to the terminal 12, neglecting the base current of the transistor 90 since this is insignificant. The voltage drop across resistors 62, B6, 106, 124, 128, 150, 144, 154, and 164 is approximately equal to the voltage drop across resistor 96 since the sum of the voltage drops across diodes 92 and 94 approximately equals the sum of the voltage drops across the base emitter of transistor 90 and any one base emitter of any of the transistors on base line 51. By selecting the ratio of resistor 96 to resistor 86 to be one half, the current ratio of the collector current of transistor 52 to the collector current of 84 is assured to be two. Also, since the collector current in transistor 84, or that current through resistor 96, is independent of temperature, the current in resistors 62, 86, 106, 124, 128, 150, 144, 154 and 164 is also independent of temperature. Therefore, each of the transistors 50, 52, 104, 122, 126, 148, 142, 152 and 162 whose bases are connected to the base line 51 are constant current source. Furthermore, the current flowing in the Zener diode 58 is exactly constant since the collector current of transistor 50 does not vary with temperature and the current in resistor 74 is constant. This is important to insure that there does not exist any voltage variation across the Zener diode 58 due to the finite dynamic impedance of this Zener diode.

The transistor 90 supplies base current to the base line 51 and to the transistors 50, 52, 104, 122, 126, 148, 142, 152 and 162 without loading the network including the diodes 92 and 94 and resistor 96. This connection greatly reduces any current variation in the base line 51 connecting the bases of these transistors from feeding back and effecting current flow in the diodes 92 and 94 since such variation as is fed back is divided by the beta of the transistor 90. The current in the collector of the transistor 84 is constant even though the beta of the transistor 84 may vary widely, due to the connection of the transistors 76 and 84 as described.

As has been stated, the zero-temperature coefficient circuit 59 including the resistors 66 and 68 should not be loaded. By connecting the base of the transistor 98 to the junction of the resistors 66 and 68 and by connecting the emitter of the transistor 98 to the base of the transistor 100, very little loading is supplied to the zero-temperature coefficient circuit 59. Furthermore, the voltage at the base of the transistor 110 is equal to the voltage at the base of the transistor 98 as a result of the differential amplifier employing negative feedback. This is accomplished as follows: As noted above, the transistor 104 is a constant current source since the current through the resistor 106 is kept constant. Since the current through the resistor 150 is also constant, the current through the resistor 146 is constant. The base-to-emitter drop in the transistor 119 is balanced by the base-to-emitter drop in the transistor 112, whereby the voltage across the resistor 108 is the same as the voltage across resistor 146 and thus the current through resistor 108 is constant. The DC current entering the collector of transistor 102 is ratioed by one half to that collector current in transistor 104. Furthermore, the collector current for the transistor 112 is fixed by the transistor 126. Since the current in resistor 108, the current in transistor 1 12, and the current in transistor 104 are each referenced to one common reference voltage, no unbalance of the differential amplifier comprising the transistors 98, 100, 102, and 110 can result due to variation in the one common reference voltage located across resistor 96. This is referred to as current source tracking.

An amplifying loop exists including a portion of the differential amplifier comprising the transistors 98, 100, 102 and 110. This amplifying loop comprises the transistor 110 and the transistor 102, the transistor 112, the diode 114, the transistor 120, the external resistor 18 with divider resistor 24 to ground and back to the base 110. This amplifying loop is, in effect, an operational amplifier whose voltage at the emitter of the transistor 120 can be whatever voltage that is desired, depending on the ratio of the resistor 18 to resistor 24, even though the voltage at the base of the transistor 110 remains at the voltage at the junction of the resistors 66 and 68 as stated above. The voltage at the terminal 20 will be equal to the voltage across the load 28 and, by choice of the resistors 18 and 24, the voltage at the terminal 20 can be fixed.

The amplifying loop operates as follows: Let it be assumed that the voltage on the base of the transistor increases, that is, that it becomes less negative than its fixed value, whereby the base of the transistor 110 is at a higher voltage than the base of the transistor 98. The current flow in the transistors 102 and 100 is no longer balanced; transistor 102 draws more current. Since transistor 104 is a constant current source, less current flows through the transistor 100. But the current in the resistor 108 is also constant whereby less current flows to the emitter of the transistor 112. This decreases the current at the base of the transistor since the transistor 126 is a constant current source. This causes less collector-toemitter current to flow in the transistor 120. Since the transistor 122 is a constant current source, more current flows through the resistors 18 and 24 forcing the voltage on the base of the transistor 110 to decrease opposing the original increase and causing the voltage at the bases of the transistors 98 and 110 to be equal. To prevent oscillations from being generated in this negative feedback circuit, the resistor 116 and the external capacitor 36 are connected between the collector of the transistor 112 at which point the greatest impedance appears and ground. These two elements force a low impedance to occur at the frequency at which this loop may oscillate such that the amplifier open loop gain is less than one when the overall open loop phase equals or exceeds 360. However, this loop has very high direct-current amplification. The resistor 116 and the capacitor 36 being, in effect, alow pass circuit, this circuit in conjunction with the high collector impedance of transistor 112 also has noise-filtering properties which is advantageous since the Zener diode 58 produces noise that requires filtering.

The two transistors 138 and 136 comprise another differential amplifier and the voltage on the base of the transistor 136 is equal to the voltage at the base of the transistor 138 during normal operation. This voltage is obviously the same as that on the emitter of the transistor 120.

As will be seen, the base of the transistor 136 is connected to the voltage-sensing terminal 30, to which one terminal of the load 28 and the filtering capacitor 34 is connected. The resistor 156 which is connected to the collector of the transistor 138 has a constant current flowing through it due to the operation of the transistors 148 and 142 and the resistors 150 and 144 and the transistors 119 and 118 and the resistor 146, in a manner similar to the mechanism that allows the current in the resistor 103 to be constant. The transistor 152 is a constant current source for the emitters of the two transistors 136 and 138. Also, the transistor 162 is a constant current source for the transistor 1 l8, and the current in the collector of transistor 152 is twice that of the current in the collector of transistor 138. Each current is referenced to one common reference. Therefore, there can be no change in the offset voltage of the differential amplifier comprising the transistors 136 and 138 due to the change in the reference voltage across the resistor 96.

The differential amplifier comprising the transistors 136 and 13% operates like the differential amplifier comprising the transistors 100, 102, 98 and 110. That is, the voltage at the base of the transistor 136 is always approximately equal to the voltage at the base of the transistor 138 since only at this relationship of these voltages is the differential amplifier, includ ing the two transistors 136 and 138, balanced. This is true due to the following action of the differential amplifier comprising the two transistors 138 and 136. Let it be assumed that the voltage at the base of the transistor 136 rises (towards zero), that is, becomes more positive with respect to the base of transistor 138. Then, the transistor 136 draws more current. Since the transistor 152 is a constant current device, less current flows into the collector of the transistor 138. Since the current in the resistor 156 is constant, more current flows through the transistor 118. Since the current through the balancing value of voltage on the base of transistor 138. The {amplifying loop, in the case of the last-mentioned differential amplifier, comprises the transistor 136, the emitter to collector of the transistor 138, the emitter to collector of the transistor 118, the base of the transistor 158, the base of transistor 166, the collector of the transistor 166 and back to the base of the transistor 136. Therefore, if the voltage on the base of the transistor 136 varies from the value of the voltage on the base of transistor 138, it is brought back to the same value by this amplifying loop. The capacitor 34 in conjunction with the load resistor 28 can be used to prevent oscillation of this loop. in addition, the capacitor 174 in conjunction with the high impedance at the base of the transistor 158 can also be used as a means to stabilize this amplifier.

Ripple voltage may occur in the described voltage regulator due to induction from nearby electrical devices causing ripple voltage in the source that is applied to the supply terminal 12. This ripple voltage is reduced not only by the filtering action of the capacitors 34 and 36 but also by so connecting the several transistors that experience ripple voltage, in the described regulator, in such a manner as to reduce the ripple. When the impedance looking into the base of a transistor is low, the impedance of that transistor looking into its collector is high. With the transistors so connected, ripple applied to the terminal 12 or collector base junctions must experience a large impedance to the output terminal and thus the ripple is reduced. Therefore, those transistors which experience ripple in the described voltage regulator are so connected as to have a low base impedance. The transistors that have ripple applied to their collectors include the transistors which are connected to the base line 51 comprising the transistors 50, 52, 104, 122, 126, 148, 142 and 152, as well as the transistors 90, 118 and 84. It is not practical to apply a large capacitor to a chip to produce this altemating-current grounding of the base of the listed transistors. The bases of the transistors which are connected to the base line 51 have low alternating-current impedance to ground since the emitter of the transistor 90 to which the base line 51 is connected has low altemating-current impedance (characteristic of emitter followers). Furthermore, the base impedance of the transistor 90 is low whereby its collector impedance is also high. Similarly, the collector impedance of the transistor 84 is high since its base is connected to the emitter of the transistor 76. The collector impedance of transistor 118 is also high since it is connected to the emitter of transistor 119. Of the mentioned transistors, transistors 152, 122 and 50 will contribute the most ripple and it is especially important the the base impedance of these transistors be small. The base of the transistor 166 is at a relatively low impedance, which causes the transistor 166 to contribute a minimum of ripple. The transistors 98 and 110 have low base current whereby they tend to prevent offset voltages from changing from base current variations due to the temperature changes applied to the chip. Similarly, transistors 136 and 138 will not contribute offset voltages due to base current changes as there are no base resistors and therefore no base current dependent voltage drops.

Overcurrent protection is built into the described regulator. This overcurrent protection includes the resistor 14 and operates as follows: Let it be assumed that the load 28 demands an excessive amount of current. This current mainly flows through the collector-to-emitter path of the transistor 166. This excessive current, therefore, flows through the resistor 14 producing a voltage drop therein in a direction in the loop from the base of the transistor 158, through the four diodes 160, 168, 170 and 172, the resistance 14, the emitter to base of the transistor 166, and the emitter to base of the transistor 158, so as to reduce current flow in the transistors 158 and 166. However, the voltage across the resistor 14 has no effect on the current flow in the transistors 158 and 166 until this voltage across the resistor 14 plus the base emitter forward voltage drops of transistors 158 and 166 overcomes the forward voltage threshold of the four diodes 160, 168, 170 and 172. Then, as the current flow through the transistor 166 and, therefore, the voltage drop in the resistance 14 exceeds this forward threshold, more base current to transistor 158 is denied and the transistors 158, 166 are biased towards constant conduction, maintaining the current flow therethrough that is supplied to the load. When the output is short circuited, protection not only for excessive current, but also protection for momentary excessive voltages are included.

This protection is required when the terminal 32 is grounded and comprises the diodes 132 and 134 and the transistor 130. Let it be assumed that the terminals 30 and 32 are short circuited to the terminal 26. Then the voltage at the base of the transistor 136 goes to zero. But the emitter of the transistor tries to maintain the original output voltage value. Therefore, if protection were omitted, the voltage at the emitter of the transistor 120 would be applied across the base to emitter of the transistor 138 and to the emitter to base of the transistor 136 which would break down the base emitter of transistor 138 and could destroy the transistor 138. The protection includes means for reducing the voltage at the emitter of the transistor 120 when such a short circuit occurs. When the terminals 30 and 32 are grounded, the forward threshold of the diode 132 and the base-emitter of the transistor are forced active rendering both conductive. The emitter current and thus the collector current of transistor 130 flows to the base of transistor 120, making transistor 120 conductive thereby providing sufficient current to supply the constant current source 122. Then, the voltage across the resistors 18 and 24 must reduce to zero since there is no current flow therethrough. Thus, the maximum voltage which appears across the base of transistor 136 and the base of the transistor 138 is equal to the forward voltage drop across diode 132 plus the base emitter voltage drop across transistor 130. The diode 132 is necessary to prevent forward bias of the base collector junction of the transistor 130 due to the base-emitter voltage drop of transistor 120.

An electronic tumoff is provided for the described voltage regulator. When a negative voltage is applied to the base of the transistor 82, the transistor 82 becomes conductive and the collector current from the transistor 82 flows therethrough satisfying the current requirement of the current source including transistor 52. As a result, there is no path for the base current of the transistor 84 and current will cease to flow through the transistor 84 turning it off. Therefore, a negative pulse on the terminal 40 will turn the regulator off for the duration of the pulse. The resistor 88 is provided to prevent unintentional turning off of the regulator as by an induced current applied to the base of the transistor 82. At least l00 pA of base drive is required to enter electronic shutdown. When the electronic shutdown is used, all the voltages in the regulator go essentially to zero (excluding the start" circuit). The large capacitor 34 will tend to discharge through the base to emitter path of the transistor 136, the emitter to base path of the transistor 138, the resistors 18 and 24 to ground, reverse biasing the emitter to base of the transistor 136 causing Zener current to flow therethrough and degrading the transistor 136. The diode 134 is provided to bypass the transistors 136 and 138 to prevent damage to the transistor 136 when the electronic shutdown is used.

The advantages of the described negative voltage regulator comprise: (1) temperature compensation for the built-in standard reference voltage is provided, (2) high ripple rejection is provided by this regulator, (3) short circuit protection (including current limiting) is built into the regulator, (4) electronic shutdown is included and also electronic shutdown protection is included in the circuit, (5) a very low output impedance in the order of 0.02 ohms is provided by this regulator, (6) all of the described voltage regulator except the elements outside of the dotted rectangle in the FIGURE can be put on a chip which measures 0.063 by 0.075 inches, (7) the described regulator can supply up to one-half an ampere, it being assumed that the voltage across the transistor 166 averages such that the power dissipation is not excessive, and (8) good frequency performance of the output impedance up to 10,000 cycles per second load variation is provided.

What is claimed is:

1. A voltage regulator comprising means for providing a reference voltage which is substantially insensitive to changes in temperature,

said reference voltage means comprising two branch circuits which are connected in shunt with each other, one of said branch circuits including an element which has a positive temperature coefficient of resistance, the other of said branches including a resistor and an element which has a negative temperature coefficient of voltage, one of said elements being a voltage standard means whose voltage varies to a slight extent with current flow therethrough, said voltage reference means further including a constant current means in series with said two branches, and means for causing the current flow in said resistor to control the current flow of said constant current source,

a direct-current voltage changer connected to said voltage reference means in a substantially nonloading manner for changing the voltage provided by the reference means to a desired output voltage,

means for supplying current to load terminals at such changed voltage,

means coupling said voltage changer to said means for supplying current for controlling the current supplied to said load terminals by said current supplying means, and

means to apply the voltage across said load terminals to said coupling means whereby said coupling means controls the current supplied by said current supplying means to said load terminals.

2. The invention as expressed in claim 1 in which said direct-current voltage changer comprises a differential amplifier which includes two transistors each including a base and an emitter and a collector, means for connecting said emitters together, means for unloadingly coupling the base of one of said transistors to said reference voltage means, a constant current source connected to supply constant current to said emitters and a second constant current source connected to supply current to the collector of the other transistor.

3. The invention as expressed in claim 2 in which a directcurrent-amplifying loop is provided including said other transistor.

4. The invention as expressed in claim 3 in which said amplifyin g loop includes at least a third transistor having an emitter and means for connecting a resistor from the emitter of the third transistor to the base of the other transistor whereby the reference voltage applied to the base of the first transistor appears as a different voltage at the emitter of the third transistor.

5. The invention as expressed in claim 4 wherein said coupling means includes at least a fourth and a fifth transistor, each having a base, a collector and an emitter, said emitters of said fourth and fifth transistors being connected together, means for supplying a constant current to said emitters of said fourth and fifth transistors, means that are connectable from the base of said fourth transistor to the emitter of said third transistor and a constant current source connected to the collector of said fourth transistor and means to connect the base of said fifth transistor to a load, all said constant current sources being controlled by said first mentioned resistor.

6. The invention as expressed in claim 5 in which a directcurrent-amplifying loop is provided in said coupling means which includes said fifth transistor.

7. The invention as expressed in claim 5 in which said collector of said fourth transistor is connected to control the current flow through said means for supplying current to said load terminals.

8. The invention as expressed in claim 5 in which said transistors whose emitters as connected together are NPN transistors and in which said means to supply current comprises a source whose positive terminal is grounded.

9. The invention as expressed in claim 2 in which said constant current device includes a sixth transistor having an emitter and a resistor connected between said emitter of said sixth transistor and a supply terminal and means to keep the voltage drop across said resistor constant.

10. The invention as expressed in claim 9 in which said means to keep said voltage drop constant comprises a connection to said reference voltage means.

11. The invention as expressed in claim 10 in which said voltage drop constant producing means includes a seventh transistor and which means are provided to shut down said voltage regulator by rendering said seventh transistor nonconductive.

12. The invention as expressed in claim 9 in which the base impedance of at least said sixth transistor is low whereby ripple in the output of said voltage regulator is reduced.

13. A negative voltage regulator comprising means for providing a negative reference voltage with respect to a reference point which is substantially insensitive to changes in temperature,

a direct-current voltage changer having two input connections and an output connection and comprising NPN transistors,

one of said input connections being connected to said voltage reference means in a substantially nonloading manner for changing the voltage provided by said reference means to a desired voltage,

said voltage changer including a feedback circuit between the output of said voltage changer and an input thereto, said feedback circuit including a PNP transistor,

an output differential amplifier comprising NPN transistors,

means to maintain the two inputs of said differential amplifier at the same voltage,

means coupling the output of said voltage changer to an input of said differential amplifier,

output means for said voltage regulator comprising at least one NPN transistor for supplying load terminals,

means to couple the output of said differential amplifier to said output means comprising a PNP transistor, and

means to apply a voltage derived from said load terminals to the other input terminal of said differential amplifier whereby the voltage on said load terminals is kept equal to the voltage on said one terminal of said differential amplifier. 

1. A voltage regulator comprising means for providing a reference voltage which is substantially insensitive to changes in temperature, said reference voltage means comprising two branch circuits which are connected in shunt with each other, one of said branch circuits including an element which has a positive temperature coefficient of resistance, the other of said branches including a resistor and an element which has a negative temperature coefficient of voltage, one of said elements being a voltage standard means whose voltage varies to a slight extent with current flow therethrough, said voltage reference means further including a constant current means in series with said two branches, and means for causing the current flow in said resistor to control the current flow of said constant current source, a direct-current voltage changer connected to said voltage reference means in a substantially nonloading manner for changing the voltage provided by the reference means to a desired output voltage, means for supplying current to load terminals at such changed voltage, means coupling said voltage changer to said means for supplying current for controlling the current supplied to said load terminals by said current supplying means, and means to apply the voltage across said load terminals to said coupling means whereby said coupling means controls the current supplied by said current supplying means to said load terminals.
 2. The invention as expressed in claim 1 in which said direct-current voltage changer comprises a differential amplifier which includes two transistors each including a base and an emitter and a collector, means for connecting said emitters together, means for unloadingly coupling the base of one of said transistors to said reference voltage means, a constant current source connected to supply constant current to said emitters and a second constant current source connected to supply current to the collector of the other transistor.
 3. The invention as expressed in claim 2 in which a direct-current-amplifying loop is provided including said other transistor.
 4. The invention as expressed in claim 3 in which said amplifying loop includes at least a third transistor having an emitter and means for connecting a resistor from the emitter of the third transistor to the base of the other transistor whereby the reference voltage applied to the base of the first transistor appears as a different voltage at the emitter of the third transistor.
 5. The invention as expressed in claim 4 wherein said coupling means includes at least a fourth and a fifth transistor, each having a base, a collector and an emitter, said emitters of said fourth and fifth transistors being connected together, means for supplying a constant current to said emitters of said fourth and fifth transistors, means that are connectable from the base of said fourth transistor to the emitter of said third transistor and a constant current source connected to the collector of said fourth transistor and means to connect the base of said fifth transistor to a load, all said constant current sources being controlled by said first mentioned resistor.
 6. The invention as expressed in claim 5 in which a direct-current-amplifying loop is provided in said coupling means which includes said fifth trAnsistor.
 7. The invention as expressed in claim 5 in which said collector of said fourth transistor is connected to control the current flow through said means for supplying current to said load terminals.
 8. The invention as expressed in claim 5 in which said transistors whose emitters as connected together are NPN transistors and in which said means to supply current comprises a source whose positive terminal is grounded.
 9. The invention as expressed in claim 2 in which said constant current device includes a sixth transistor having an emitter and a resistor connected between said emitter of said sixth transistor and a supply terminal and means to keep the voltage drop across said resistor constant.
 10. The invention as expressed in claim 9 in which said means to keep said voltage drop constant comprises a connection to said reference voltage means.
 11. The invention as expressed in claim 10 in which said voltage drop constant producing means includes a seventh transistor and which means are provided to shut down said voltage regulator by rendering said seventh transistor nonconductive.
 12. The invention as expressed in claim 9 in which the base impedance of at least said sixth transistor is low whereby ripple in the output of said voltage regulator is reduced.
 13. A negative voltage regulator comprising means for providing a negative reference voltage with respect to a reference point which is substantially insensitive to changes in temperature, a direct-current voltage changer having two input connections and an output connection and comprising NPN transistors, one of said input connections being connected to said voltage reference means in a substantially nonloading manner for changing the voltage provided by said reference means to a desired voltage, said voltage changer including a feedback circuit between the output of said voltage changer and an input thereto, said feedback circuit including a PNP transistor, an output differential amplifier comprising NPN transistors, means to maintain the two inputs of said differential amplifier at the same voltage, means coupling the output of said voltage changer to an input of said differential amplifier, output means for said voltage regulator comprising at least one NPN transistor for supplying load terminals, means to couple the output of said differential amplifier to said output means comprising a PNP transistor, and means to apply a voltage derived from said load terminals to the other input terminal of said differential amplifier whereby the voltage on said load terminals is kept equal to the voltage on said one terminal of said differential amplifier. 